It is known that ring-opened polymers are produced from cycloolefins by the use of a metathesis polymerization catalyst system. Therefore, a process has been proposed to obtain a molded polymer article by carrying out the polymerization and molding of a metathesis polymerizable cycloolefin, such as dicyclopentadiene (DCPD), in one step in a mold using a metathesis polymerization catalyst. More particularly, a process has been proposed to obtain a molded polymer article, taking advantage of the fact that a metathesis polymerization catalyst system is composed of two components consisting of a catalyst component such as tungsten chloride and an activator component such as an alkylaluminum, by using two solutions, each of which contains one of the above components and a monomer, quickly mixing the solutions and injecting the mixture into a mold (for example, U.S. Pat. No. 4,400,340).
Such processes are very attractive from an industrial viewpoint because large-sized molded articles having good mechanical properties can be produced, using an inexpensive low-pressure mold. However, it has been found with the progress of practical application that some improvements are desirable.
One of the required improvements is the reduction of residual monomers in the molded article. In general, unreacted monomers are left in a molded article produced by the simultaneous polymerization and molding of metathesis polymerizable cycloolefins. Metathesis polymer molded article frequently contains up to several percent of residual monomer. Since cycloolefins generally have a characteristic unpleasant odor, the molded article also emits the particular odor. Furthermore, the residual monomer decreases the heat-deformation temperature of the molded article by its plasticizing action.
Accordingly, the reduction of the amount of residual monomer has become important from the viewpoint of widening the application field of the product.
U.S. Pat. No. 4,481,344 discloses that hydrocarbon compounds having a trihalogenated carbon group and hydrocarbon compounds having a halogen atom activated by a double bond at .beta.-position can be used as a residual monomer reducing agents. The inventors of the present invention have also found, independently, that carboxylic acid halides, carboxylic acid anhydrides, silicon halides and phosphorus halides also have residual monomer reducing effects.
As a result of intensive investigation on the mechanism of the effect of the above compounds to reduce the residual monomer content, the following facts have been found.
The transition metal element forming the catalyst of a metathesis polymerization catalyst system is generally used in the state of its highest atomic valence. However, the element is reduced by the action of an activator to a state of lower atomic valence. This reduction can be observed, for example, by the fading of the dark red purple color of a catalyst based on tungsten hexachloride to an extremely light color upon mixing with an alkylaluminum-based activator.
When the system contains a halogenated compound, e.g. as taught by U.S. Pat. No. 4,481,344, it is believed that a redox system is formed between that compound and the reduced transition metal to cause the oxidation of the transition metal back to its original valence, and the reduction of the halogenated compound into a halide anion and a residue remaining in the form of a radical formed by the extraction of halogen. This reaction can be observed also by the fact that the red purple color of a molded polymer article is intensified as compared with a molded article lacking the halogenated compound.
There are at least two possible explanations for the reduction of residual monomers by the redox reaction. One of the explanations is the activation of the metathesis polymerization capability of the reoxidized transition metal. Another possible explanation is that the radical produced by reduction of the halogenated compound decreases the remaining monomer by radical polymerization of the cycloolefin. The correct explanation has not been clearly confirmed.
For the further clarification of the mechanism, tungsten hexachloride was solubilized by complexing with a phenolic compound. The solubilized tungsten hexachloride and an amount of dichlorodiphenylmethane equivalent to that used as a typical monomer-reducing agent according to U.S. Pat. No. 4,481,344 were added to methyl methacrylate and heated. No radical polymerization was observed. On the contrary, when tungsten pentachloride solubilized in the same manner was heated in methyl methacrylate together with dichlorodiphenylmethane of an amount equivalent to the tungsten content of the solubilized tungsten chloride, the methyl methacrylate was polymerized.